The Merrimack is an important regional focus in both New Hampshire
and Massachusetts. In New Hampshire, the central-southern part of
the state is known as the Merrimack Valley Region, and in
Massachusetts, the "Merrimack Valley" refers to
a cluster of towns and small cities in the northeastern part of the
state.

Several U.S. naval ships have been named the USS Merrimack and USS
Merrimac in honor of this river.

History and details

Prior to
glaciation, the Merrimack continued its southward course far beyond
the present day New Hampshire-Massachusetts border to enter the
Atlantic Ocean near Boston. Upon
the glacier's retreat, debris deposited north of Boston filled the
lower Merrimack Valley, redirecting the river into its current
northeast bend at Lowell. The Neville archaeological site is
located along the river's banks in New Hampshire.

Merrimack River watershed

The total watershed of the river is approximately , covering much
of southern New Hampshire and a portion of northeastern
Massachusetts. On its banks are a number of cities built to
take advantage of water power in the 19th Century, when textile
mills dominated the New England economy: Concord, Manchester, and Nashua in New Hampshire, and Lowell, Lawrence, and Haverhill in Massachusetts.At the mouth of the
river is the small city of Newburyport. Prior to the construction of the Middlesex Canal, Newburyport was an
important shipbuilding city, in a location to receive New Hampshire
timber that had been floated downriver.

According to Joseph B. Walker, relying on Chandler Eastman Potter's
The History of Manchester (1856), Merremack
contains the elements merruh ("strong") and auke
("place"—a recognizable locative ending),
and means "the place of strong current,- a term not inappropriate,
when we consider ... the river's rapids ...." Potter was an
authority on native American affairs in colonial New England. By
contrast, in A Week on the Concord
and Merrimack Rivers, Henry
David Thoreau implies that "its name signifies the Sturgeon
River."

Merrimack River in flood, October
2005, Manchester, NH

Walker
goes on to cite spellings of Merimacke, Merimack and Merrimacke in
"the colonial records of Massachusetts", as well as the Merrimake
and Merrymake of a 1721 land grant at Penacook,
New Hampshire.William Wood's New England's
Prospect of 1634 calls the river the Merrimacke and locates it
eight miles beyond Agowamme (Ipswich, Massachusetts). It hosts, he says, "Sturgeon, Sammon and
Basse, and divers other kinds of fish."

Merrimac,
Massachusetts, settled in 1638 and originally part of Amesbury,
Massachusetts, was called West Amesbury until 1876, at which time
it adopted its current name and spelling.Merrimack,
New Hampshire was incorporated in 1746, spelling its name
"Marrymac" in the record of its first town meeting. It is
referred to as Merrimac into the early 19th century: in the 1810
decennial census, it was spelled Merrimac, but in the 1820 and
afterwards, Merrimack.

In 1914, US Congressman John Jacob
Rogers (MA) petitioned that the official spelling be
Merrimack.

May 2006 Flooding

While the
Merrimack River is prone to minor flooding,
on May 15, 2006 rainfall
raised the river more than above flood stage, forcing evacuations,
damaging property, and breaking the main sewage pipeline in the
city of Haverhill, Massachusetts, dumping 35 million gallons of raw sewage waste
into the river per day. Reports of total rainfall vary, but
most areas appear to have received around a foot of rain with some
areas receiving as much as .

According to The Boston Globe, around 1,500 people evacuated their
homes to escape the flood.

This
flood also prompted the city of Lowell, Massachusetts to install a modern (albeit temporary) flood
control gate comprising square steel beams at the site of the
historic Francis Gate, a 19th and
20th century wooden flood gate. When lowered, the Francis
gate seals the city's canal system off from its source on the
Merrimack. The Great Gate, as it is also called, was built in 1850
under the direction of James B.Francis. Considered unnecessary
when it was first constructed, "Francis' Folly" first saved the
city in 1852 and subsequently in 1936.

Other flooding events

The most significant flood in the recorded history of the Merrimack
was in March 1936, when a double flood of rain and melting snow and
ice swelled the Merrimack at Lowell to , higher than the 2006
flood. The Jack Kerouac book
Doctor Sax is set during this
event.

In addition to the 1936 flood, the 1852 flood, and the Mother's Day
Flood of 2006, the New
England Hurricane of 1938 and a flood in April 2007 round out
the river's most serious flood events, measured at Lowell. The
Francis Gate had been left in place after being dropped in 1936, so
it prevented flooding in 1938 as well. In 2007, the steel beam
system was again assembled in place.